Abstract: The Three Gorges Reservoir adopts a hydrological regime of 175 m water level in winter and 145 m water level in summer, and has formed a reservoir inundated zone with an area of 348 km² since 2007. This change leads to the disappearance of original plant species and plant communities, and the formation of permanent waters and the appearance of novel plant communities that gradually adapt to the environment of riparian zone. We analyzed the plant species diversity in the inundated zone and riparian zone of the Three Gorges Reservoir Area (TGRA) before and after the operation of the reservoir. Results showed that: (1) There were 769 vascular plant species, belonging to 400 genera of 121 families in the inundated area before damming. Perennial herbs, annual herbs and shrubs were co-dominated in this area. After damming, the vascular plant species dropped dramatically to about 300, with shrub losing its dominant role. The percentage of annuals increased from 26.42% to 45.46%, while perennials decreased from 44.43% to 32.47%. Woody plants (trees and shrubs) decreased from 23.71% to 15.15%. (2) In the first three years after the formation of the riparian zone (2008-2010), species decreased persistently. Some species (such as Cynodon dactylon and Xanthium sibiricum) showed advantages in competition after several times of intense submergence. (3) Species diversity increased with elevation in the riparian zone after damming. Species richness index showed an exponential rise, with 8 at 158 m, 10 at 164 m and 13 at 170 m. Shannon index showed an S rise, with two inflection points at 150 m and 171 m. After 8 years of formation of the reservoir riparian zone, the structure and function of plant communities is still changing and far from steady state, and further studies are needed to reveal temporal and spatial trends of plant communities and underlying mechanisms.

Key words: cucumber, root border cell, allelochemical stress., nitric oxide (NO), Eupatorium adenophorum extract